Targeted delivery of colloids by swimming bacteria

• Published in: Nature communications Vol. 4; no. 1; p. 2588
• Main Authors: Koumakis, N., Lepore, A., Maggi, C., Di Leonardo, R.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08-10-2013; Nature Publishing Group; Nature Pub. Group
• Subjects: 631/57; 631/61; Colloids; Drug Delivery Systems; Escherichia coli - physiology; Escherichia coli - ultrastructure; Humanities and Social Sciences; Likelihood Functions; Locomotion; Microscopy; multidisciplinary; Optical Tweezers; Science; Science (multidisciplinary); Silicon Dioxide - chemistry; Stochastic Processes; Water
• ISSN: 2041-1723
• DOI: 10.1038/ncomms3588

The possibility of exploiting motile microorganisms as tiny propellers represents a fascinating strategy for the transport of colloidal cargoes. However, delivery on target sites usually requires external control fields to steer propellers and trigger cargo release. The need for a constant feedback mechanism prevents the design of compact devices where biopropellers could perform their tasks autonomously. Here we show that properly designed three-dimensional (3D) microstructures can define accumulation areas where bacteria spontaneously and efficiently store colloidal beads. The process is stochastic in nature and results from the rectifying action of an asymmetric energy landscape over the fluctuating forces arising from collisions with swimming bacteria. As a result, the concentration of colloids over target areas can be strongly increased or depleted according to the topography of the underlying structures. Besides the significance to technological applications, our experiments pose some important questions regarding the structure of stationary probability distributions in non-equilibrium systems.
Transport of colloidal cargoes to target sites can be done by controlling active carriers, like self-propelled bacteria, under external stimuli. Koumakis
et al.
show that bacteria can autonomously achieve the same goal when moving over pre-designed asymmetric microstructures.